Impedance Spectroscopy and Photovoltaic Effect of Oxygen Defect Engineering on KNbO 3 Ferroelectric Semiconductors
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https://doi.org/10.1007/s11664-020-08334-0 2020 The Minerals, Metals & Materials Society
Impedance Spectroscopy and Photovoltaic Effect of Oxygen Defect Engineering on KNbO3 Ferroelectric Semiconductors FEI HAN,1 YUJIE ZHANG,1 CHANGLAI YUAN,1,2,4,5 XIAO LIU,1 BAOHUA ZHU,1,2,6 FEI LIU,1 LIUFANG MENG,1 JIANG WANG,1 CHANGRONG ZHOU,1,2 and GUANGHUI RAO1,2,3,7 1.—College of Material Science and Engineering, Guilin University of Electronic Technology, Guilin 541004, People’s Republic of China. 2.—Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, Guilin 541004, People’s Republic of China. 3.—Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China. 4.—e-mail: [email protected]. 5.—e-mail: [email protected]. 6.—e-mail: [email protected]. 7.—e-mail: [email protected]
Perovskite-oxide (1 x)KNbO3-xBaCo1/2Nb1/2O3 d (KN-BCN; x = 0.00–0.20) ferroelectric semiconductor ceramics with oxygen defects are successfully prepared via a conventional solid-state sintering method. X-ray diffraction data indicate that the crystal symmetry evolves from orthogonal to tetragonal at increasing x values. Raman spectroscopic analysis confirms the long-range polarization of all compositions. X-ray photoelectron spectroscopy shows that the detailed chemical formula of 0.90KN-0.10BCN ceramics is 0.90KNbO30.10BaCo1/2Nb1/2O2.90. Room-temperature ferroelectricity weakens when the x value increases. The optical band gap narrows from 3.25 eV for x = 0.00 to 1.57 eV for x = 0.20, and the minimum value of 1.28 eV occurs in the 0.90KN-0.10BCN ceramic. Impedance analysis illustrates that the conduction mechanism of grains is mainly internal electron conduction, and that of the grain boundary is intrinsic conduction. The conducting mechanism of the ceramic system follows ohmic behavior by log I–log U curves. The maximum short-circuit photocurrent density and open-circuit photovoltage are 6.68 nA cm 2 and 0.80 V, and stable output is maintained. The KN-BCN ceramic system can be used in photovoltaic materials. Key words: Perovskites, band gap, ferroelectric semiconductors, impedance spectroscopy
INTRODUCTION ABO3-type perovskite oxides have attracted interest because of their optical properties that are essential to photocatalysis, photovoltaics, and solar cells.1–5 Ferroelectric semiconductor perovskite materials have been widely studied as candidate optoelectronic materials. As an excellent photoresponsive material, a ferroelectric internal electric field is expected to greatly improve the separation of electron–hole pairs and efficiency.6 However, most
(Received February 5, 2020; accepted July 14, 2020)
ferroelectrics exhibit optical band gaps that are usually larger than 3 eV and only absorb in the ultraviolet range. Therefore, effective methods for regulating band gaps are urgently needed. At present, halides and oxides in perovskite structural materials have attracted considerable attention. However, perovskite halides are extremely sensitive to the effects of temperatu
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